Method for making herringbone gears

ABSTRACT

A method of manufacturing herringbone gears using an injection molding process is provided. The process involves the use of two separable mold halves each of which include a mold cavity for molding one half of the gear. Moldable material is injected into the mold halves when they are in a sealing abutting engagement. After the material solidifies, the mold halves are separated and the gear is simultaneously unscrewed from each mold cavity.

FIELD OF THE INVENTION

The present invention relates generally to gear pumps utilizing meshingherringbone gears. More specifically, the present invention relates toan improved method and apparatus for manufacturing herringbone gears andgear pumps that incorporate the herringbone gears made in accordancewith the present invention.

BACKGROUND OF THE INVENTION

Gear pumps are positive displacement pumps utilizing a set of gears asthe displacement device. The most common type of gear used in fluidpumps is the helical gear. Helical gears are preferred because of theirquiet operation, hydraulic efficiency, conjugate mechanical motion,constant sealing of the surfaces between the mating gear flanks and theminimum entrapment of fluid between the teeth that are in contact.Further, the helical gear, with its angled teeth, typically has a higherload carrying capacity than the spur gear, which has straight teeth.Because helical gears tend to run more smoothly than spur gears, helicalgears can normally operate at faster speeds.

However, one substantial drawback with the helical gear is the creationof an axial thrust which results from the helical lead or angle of thegear teeth. In operation, the axial thrust must be absorbed by thebearings that support the gear shafts. As a result, relatively expensivebearings are required to absorb these axial forces.

In order to eliminate the axial thrust associated with the use ofhelical gears, herringbone gears were developed. A herringbone gear isconstructed of adjacent helical gear halves whereby the teeth of theadjacent halves are angled in an opposite direction. A comparison of twomeshing helical gear teeth 11, 12 and two meshing herringbone gear teeth13, 14 is provided in FIGS. 1 and 2 respectively. The helical gears 11,12 shown in FIG. 1 have one helical slant or angle with respect to thelongitudinal gear axis although the helical slant of the gear 11 isangled upward from left to right in FIG. 1 and, in contrast, the helicalslant of the gear 12 is angled downward from left to right in FIG. 1. Inshort, the magnitude of the helical slants of the gears 11, 12 are thesame, but in opposite directions.

In contrast, the gears 13, 14 each have two adjacent halves with helicalslants of the same magnitude but in opposing directions. The gear 13includes adjacent gear halves 15, 16. The helical slant of the gear half15 extends downward from left to right and the helical slant of the gearhalf 16 extends upward from left to right. Similarly, the gear 14includes gear halves 17, 18. The gear half 17 has a helical slant whichextends upward from left to right in FIG. 2 while the gear half 18 has ahelical slant that extends downward from left to right in FIG. 2. Themagnitude of the helical slants of the gear halves 15, 16, 17, 18 arethe same or substantially the same but the gear halves disposed at theleft in FIG. 2, specifically the gear halves 15, 17 have helical slantsthat are oppositely directed to the gear halves disposed at the right inFIG. 2, specifically the gear halves 16, 18.

By incorporating gear halves such as 15, 16 and 17, 18 which havehelical slants of the same magnitude but in opposite directions, theherringbone gears 13, 14 provide excellent power or fluid transmissionwithout an axial thrust which is the result of the helical slant of thehelical gears 11, 12 as shown in FIG. 1.

It will also be noted that the gear halves 15, 16 and 17, 18 aredisposed on opposite sides of a central plane shown at the line 19 drawnin phantom which passes through each gear 13, 14 perpendicular to thelongitudinal axes 21, 22 of the gears 13, 14 and at a mid-point alongthe longitudinal axes 21, 22 of the gears 13, 14.

However, while effective in eliminating the axial thrust imposed uponthe shaft and bearing by helical gears, herringbone gears are difficultand expensive to manufacture. Specifically, they cannot be manufacturedusing a hobbing or shaping process due to the change in direction of thehelical slant. As a result, the manufacture of herringbone gears in thepast has been labor intensive and, as a result, expensive.

One approach at alleviating this problem has been to manufacture"pseudo" herringbone gears. Pseudo herringbone gears include twooppositely angled helical gears that are coupled or attached together atthe longitudinally central plane such as 19 shown in FIG. 2. One suchmethod for manufacturing pseudo herringbone gears is disclosed in U.S.Pat. No. 4,690,009. However, the process disclosed in the '009 patent isrelatively slow and requires complex machine tools to carry out theoperation.

Currently, there is no available manufacturing process to manufactureherringbone gears using a molding method or an injection molding method.Such a method would be beneficial due to its high speed of operation andlow cost. A molding process would also result in a unitary gear insteadof two gears that are coupled or attached together. Accordingly, thereis a need in the pumping and pump manufacture industry for a method ofmanufacturing herringbone gears which utilizes a molding process.

SUMMARY OF THE INVENTION

To address the aforenoted need in the art, the present inventionprovides a method of manufacturing herringbone gears utilizing aninjection molding process. The process includes the steps of providing amold that includes two separate mold halves. The mold halves correspondto the two halves of the herringbone gear. Each mold half includes aninner mating face for sealing engagement with the inner mating face ofthe other mold half. When placed in a sealing abutting engagement, thetwo mating faces of the mold halves correspond to the central plane ofthe gear.

One of the mold halves includes a gate for injecting molding materialinto the two adjoining mold cavities when the two mold halves are pushedtogether. At least one of the mold halves is capable of longitudinalmovement along the longitudinal axis of the gear.

The method of the present invention further comprises the steps ofmoving the mold halves together to engage the inner mating faces of eachmold half, injecting molding material through the gate, allowing themolding material to solidify to form a molded herringbone gear and,simultaneously extracting the gear from the mold and opening the mold bymoving the mold halves apart. During the extraction opening step, eachgear half becomes unscrewed from its respective mold cavity as theentire gear rotates.

In an embodiment, one of the mold halves also includes an elongatedcavity disposed adjacent to the mold half cavity for accommodating agear shaft or gear axle. The method of the present invention furthercomprises the step of inserting a gear shaft through the elongatedcavity and through both mold half cavities before the molding materialis injected.

The present invention also provides an apparatus for manufacturingmolded herringbone gears. The apparatus comprises two mold halves, atleast one of which is capable of longitudinal movement along thelongitudinal axis of the gear. Other than the longitudinal movement ofat least one mold half, the mold halves are preferably constrained inall other directions. Each mold half comprises an inner mating face forsealing engagement with the opposing inner mating face of the other moldhalf. The two mating faces of the mold halves correspond to the centralplane of the gear. One of the mold halves includes a gate for injectingmolding material into the mold cavities.

In an embodiment, one of the mold halves further includes an elongatedcavity disposed along the longitudinal axis of the gear foraccommodating a gear shaft. The gear shaft may be inserted into the moldcavities before the molding material has been injected into the cavitiesand, before the molding material has hardened.

In an embodiment, an ejection or extractor tool passes through an end ofone mold half and engages the molded gear and pushes the molded gear outof said mold half as the mold is opened.

In an embodiment, one of the mold halves is slightly longer than theother mold half which results in the finished part being retained in oneof the mold halves as the mold is opened. As a result, an ejectiondevice can be utilized to reliably clear the molding apparatus forsubsequent cycles.

In an embodiment, the gate further comprises a stripper plate.

In an embodiment, the gate is further characterized as being a helicalgate having a helical lead substantially the same as the helical lead ofthe mold half on which the gate is disposed.

In an embodiment, the gate is further characterized as being a conicallyshaped gate having an interior surface that slants from an end of a moldcavity toward the longitudinal axis of the gear at an angle that issubstantially the same angle as the helical lead of the mold half ormold cavity adjacent to which the gate is disposed.

In an embodiment, each mold half is capable of longitudinal movementalong the longitudinal axis of the gear so that both mold halves may besimultaneously moved apart when the molded herringbone gear is beingejected from the mold cavities.

The present invention also provides an improved pump that includes ahousing having a pump cavity. The pump cavity accommodates two injectionmolded herringbone gears. One of the injection molded herringbone gearsis mounted on a drive axle and the second injection molded herringbonegears is in meshing engagement with the first injection moldedherringbone gear.

Each of the gears is of the same configuration as discussed above and,in a preferred embodiment, each of the gears is manufactured using aninjection molding process as discussed above.

It is therefore an object of the present invention to provide animproved method of manufacturing herringbone gears.

Another object of the present invention is to provide an improvedapparatus for manufacturing herringbone gears.

Still another object of the present invention is to provide an improvedpump incorporating injection molded herringbone gears.

Other objects and advantages of the present invention will becomeapparent upon reading the following detailed description and appendedclaims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of thepresent invention.

FIG. 1 is a perspective view of two helical gears taught by the priorart.

FIG. 2 is a perspective view of two herringbone gears taught by theprior art.

FIG. 3 is a schematic illustration of an apparatus for manufacturingherringbone gears in accordance with the method of the presentinvention.

FIG. 3A is a perspective view of a herringbone gear manufactured withthe apparatus illustrated in FIG. 3.

FIG. 4 is a sectional view of an apparatus used to manufactureherringbone gears in accordance with the present invention.

FIG. 4A is a partial sectional view taken along line 4A--4A of FIG. 4.

FIG. 5 is an illustration of the apparatus shown in FIG. 4 duringextraction of the molded herringbone gear from the apparatus.

FIG. 6 is an illustration of the apparatus shown in FIG. 4 duringextraction of the molded herringbone gear from the apparatus.

FIG. 7 is an illustration of the apparatus shown in FIG. 4 at the end ofthe extraction of the herringbone gear from the apparatus.

FIG. 8 is a sectional view of another embodiment of an apparatus formanufacturing herringbone gears in accordance with the presentinvention.

FIG. 9 is an illustration of the apparatus shown in FIG. 8 duringextraction of the herringbone gear from the apparatus.

FIG. 10 is an illustration of the apparatus shown in FIG. 8 duringextraction of the herringbone gear from the apparatus.

FIG. 11 is an illustration of the apparatus shown in FIG. 8 after theherringbone gear has been extracted from the apparatus.

FIG. 12 is an illustration of a pump made in accordance with the presentinvention incorporating the injection molded herringbone gears of thepresent invention.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 3 is an illustration of an apparatus 30 used to manufacture theherringbone gear 13 shown in FIG. 3A. Specifically, the apparatus 30includes two mold halves 31, 32 which include cavities shown at 33, 34which are used to mold the gear halves 15, 16 respectively. One of themold halves, and specifically the mold half 31 as shown in FIG. 3 iscapable of movement along the longitudinal axis 21 of the gear 13 eachmold half 31, 32 includes an inner mating face 35, 36 respectively whichare in an abutting, sealing engagement when molding material is injectedinto the cavities 33, 34 as illustrated in FIG. 4. Still referring toFIG. 3, the mold half 31 is capable of movement along the longitudinalaxis 21 only. It will be noted that both mold halves 31, 32 arepreferably restrained in all other directions.

Turning to FIG. 4, an apparatus 40 is illustrated which includes moldhalves 31, 32 in a sealing and abutting engagement. The inner matingfaces of each seal half 31, 32 are disposed along the center plane 19 ofthe gear 13 (see also FIG. 3A). The mold half 31 is attached to an endplate 37 which accommodates a gating system 38. In the embodiment 40shown in FIG. 4, the gating system includes a conically-shaped sprue 39which has an angle substantially the same or similar to the helical leadof the gear pattern of the cavity 33. In other words, the inside surfaceof the conical sprue 39 extends downward to the left in FIG. 4 atsubstantially the same angle as the slanting angle of the teeth of thecavity 33 in FIG. 4. In an alternative embodiment, the sprue 39 can havea helical configuration similar to that of the helical cavity 33. Again,the slant of the sprue 39 and the cavity 33 should be the same orsubstantially the same. In another alternative embodiment, the gatingsystem 38 should include a stripper plate to remove the gating materialprior to the opening of the mold halves 31, 32.

In the apparatus 40 as illustrated in FIG. 4, an end plate 41 isattached to the mold half 32. The conduit or cavity 42 extends throughthe end plate 41 and accommodates an ejection tool 43. An end plate 44of the ejection tool 43 abuts the end 45 of the cavity 34. After moldingmaterial has been inserted through the sprue 39 and into the cavities33, 34, the moldable material engages the end plate 44 of the ejectiontool 43. The end plate 44 preferably has a smooth surface for engagingthe gear and still more preferably, the end plate 44 is loosely attachedto the end of the ejection tool 43 so that the plate 44 can rotate asthe gear 13 is extracted from the mold halves 31, 32.

As shown in FIGS. 4-7, a shaft 51 may be inserted through the ejectiontool 43 and through both cavities 33, 34. The end 52 of the shaft 51 issupported in the sprue 39 by a slotted shaft support 53 which is shownin FIG. 4A. The slots shown generally at 54 permit the moldable materialto pass through the sprue 39 when the shaft 51 and support 53 are inplace.

To extract the gear 13 and shaft 51 from the cavities 33, 34, the moldhalves 31, 32 must be separated. In the embodiment illustrated in FIGS.4-7, this is accomplished by pulling the mold half 32, end plate 41,structural bracket 46 and end plates 47, 48 to the right as illustratedin FIGS. 5, 6 and 7. The left mold half 31 remains fixed in place. Asillustrated below with respect to FIG. 9, the ejection tool 43 moves tothe right at a slower rate than the mold half 32 and, as a result, thecavity 34 passes over the end 44 of the ejection tool 43 as illustratedin FIGS. 5, 6 and 7.

As the gear 13 is extracted from both cavities 33, 34 simultaneously,the gear rotates. As noted above, the smooth end plate 44 rotates withthe rotation of the gear 13. The shaft 51 slides through the centralbore 55 of the tool 43 as the gear 13 and shaft are extracted.

Another embodiment of the present invention is illustrated by apparatus60 in FIGS. 8-11. Again, the right mold half 32 is moved to the rightwhile the left mold half 31 remains fixed in place as illustrated inFIGS. 4-7. The two mold halves 31, 32 are separated upon rotation of thegear 61 which is meshed with the rack of teeth 62 and the rack of teeth63. When the gear 61 is rotated in the clockwise direction as shown inFIG. 8, the rack of teeth 62 is pulled to the right which, by way of itsattachment to the structural member 46, pulls the end plate 41 and rightmold half 32 to the right.

As illustrated in FIG. 9, rotation of the gear 61 causes the right sideof the mold 60 (namely the right mold half 32, plate 41, structuralsupport 46 and end structures 47, 48) to move to the right a distance orat a rate d. In contrast, because the gear 61 is meshed with the teeth63 which are fixed in space by way of the connection to the left moldhalf 31 and the support 62, the center line 66 of the gear 61 moves onlya distance or at a rate d/2 or one half the rate that the right side ofthe mold moves. Further, the ejector tool 43 is connected to the gear 61and therefore moves to the right of the rate the gear 61 moves (i.e.d/2). As the right mold half 32 moves to the right at rate d, theejector tool moves to the right at rate d/2 and the cavity 34 passesover the end plate 44 of the ejector tool 43. Further, the gear 13 ismoving to the right at the rate d/2 which caused the gear to be ejectedor rotated out of both the right mold half 31 and left mold half 32simultaneously as illustrated in FIGS. 9-11 and simultaneously as themold 60 is opened.

As illustrated in FIG. 11, a central shaft 65 may extend outward fromthe center of the extraction tool 43 to facilitate the clearing of theapparatus 60 for the next cycle.

In operation, the mold halves 31, 32 are placed together as illustratedin FIGS. 4 and 8. The molding material is then injected through the gatesystem 38. The material is allowed to solidify before the mold halves31, 32 are separated as illustrated in FIGS. 5-7 and 9-11. During theseparation of the mold halves 31, 32, the gear 13 rotates as it issimultaneously extracted from the cavities 33, 34. This, the opening orseparation of the mold halves 31, 32 causes the extraction of the gear13. The molding material must be strong enough and the helical leadslight enough to permit the simultaneous opening of the mold halves 31,32 and extraction of the gear 13.

The molding material used to fabricate the gear 13 may be athermoplastic or a melt processable metal. Suitable thermoplasticmaterials include polyphenylene sulfide, polyetheretherketone, liquidcrystal polymers, acetal resins and fluropolymers. Suitable metallicprocesses include investment casting and lost wax casting. The gearscould also be fabricated from stainless steel. Other suitable materialswill be apparent to those skilled in the art. The helical lead may varyfrom 10 inches per revolution to 30 inches per revolution depending uponthe profile/contact ratio of the gear and the strength of the moldingmaterial.

FIG. 12 illustrates a pump 70 that incorporates two molded herringbonegears 13, 14 made in accordance with the present invention. The pump 70includes a housing 71 which defines a cavity which accommodates the twomeshing gears 13, 14. The herringbone gear 14 is mounted onto a driveshaft 72 which imparts rotation to the gear 14. The meshing relationshipbetween the gear 14 and the gear 13 results in rotation of the gear 13.

From the above description, it is apparent that the objects of thepresent invention have been achieved. While only certain embodimentshave been set forth, alternative embodiments and various modificationswill be apparent to those skilled in the art. These and otheralternatives are considered equivalents within the spirit and scope ofthe present invention.

What is claimed is:
 1. A method of manufacturing a herringbone gear, thegear comprising two helical gear halves disposed along a commonlongitudinal axis and on opposing sides of a central plane extendingperpendicular to the axis, each helical gear half having a helical lead,the helical leads of the helical gear halves being substantially thesame in magnitude but opposite in direction, the method comprising thefollowing steps:providing a mold comprising two mold halvescorresponding to the two halves of the gear, each mold half comprising amold cavity corresponding to one half of the gear and an inner matingface for sealing engagement with the inner mating face of the other moldhalf, the two mating faces of the mold halves corresponding to thecentral plane of the gear, one of said mold halves comprising a gate forinjecting molding material into the mold halves, at least one of saidmold halves being capable of longitudinal movement along the axis of thegear, moving the mold halves together to engage the inner mating facesof each mold half, injecting molding material into the mold through thegate, solidifying the molding material to form the herringbone gear,extracting the gear from the mold by moving at least one mold half awayfrom the other mold half to extract the gear from the mold halves. 2.The method of claim 1 wherein the extracting step further comprises thegear rotating as the one mold half is moved away from the other moldhalf.
 3. The method of claim 1 wherein the extracting step furthercomprises each gear half rotating as the one mold half is moved awayfrom the other mold half.
 4. The method of claim 1 wherein theextracting step is further characterized as the simultaneous opening ofthe two mold halves and extraction of the gear from the two mold halves.5. The method of claim 1 wherein the extracting step further comprisesunscrewing each gear half from its respective mold half as the one moldhalf is moved away from the other mold half.
 6. The method of claim 1wherein one of mold halves further comprises an elongated cavitydisposed along the axis for accommodating a gear shaft, the methodfurther comprises the following step prior to the injectingstep:inserting a gear shaft through the elongated cavity and throughboth mold half cavities.